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Recent Results on Classifying Risk-Based Testing Approaches Michael Felderer University of Innsbruck, Austria J¨urgenGroßmann Fraunhofer FOKUS, Germany Ina Schieferdecker Fraunhofer FOKUS & TU Berlin, Germany Abstract In order to optimize the usage of testing efforts and to assess risks of software- based systems, risk-based testing uses risk (re-)assessments to steer all phases in a test process. Several risk-based testing approaches have been proposed in academia and/or applied in industry, so that the determination of principal concepts and methods in risk-based testing is needed to enable a comparison of the weaknesses and strengths of different risk-based testing approaches. In this chapter we provide an (updated) taxonomy of risk-based testing aligned with risk considerations in all phases of a test process. It consists of three top-level classes, i.e., contextual setup, risk assessment, and risk-based test strategy. This taxonomy provides a framework to understand, categorize, assess and compare risk-based testing approaches to support their selection and tailoring for specific purposes. Furthermore, we position four recent risk-based testing approaches into the taxonomy in order to demonstrate its application and alignment with available risk-based testing approaches. arXiv:1801.06812v1 [cs.SE] 21 Jan 2018 1 Introduction Testing of safety-critical, security-critical or mission-critical software faces the problem of determining those tests that assure the essential properties of the software and have the ability to unveil those software failures that harm the critical functions of the software. However, also for "normal" less critical software a comparable problem exists: Usually testing has to be done under severe pressure due to limited resources and tight time constraints with the consequence that testing efforts have to be focused and be driven by business risks. Both decision problems can adequately be addressed by risk-based testing which consider risks of the software product as the guiding factor to steer all phases of a test process, i.e., test planning, design, implementation, execution, and evaluation [1, 2, 3]. 1 Risk-based testing is a pragmatic, in companies of all sizes widely used approach [4, 5] which uses the straightforward idea to focus test activities on those scenarios that trigger the most critical situations of a software system [6]. Recently, the international standard ISO/IEC/IEEE 29119 Software Testing [7] on testing techniques, processes, and documentation even explicitly specifies risk consid- erations to be an integral part of the test planning process. Because of the growing number of available risk-based testing approaches and its increasing dissemination in industrial test processes [8], methodological support to categorize, assess, compare, and select risk-based testing approaches is required. In this paper, we present an (updated) taxonomy of risk-based testing that pro- vides a framework for understanding, categorizing, assessing, and comparing risk-based testing approaches and that supports the selection and tailoring of risk-based testing approaches for specific purposes. To demonstrate the application of the taxonomy and its alignment with available risk-based testing approaches, we position four recent risk-based testing approaches, i.e., the RASEN approach [9], the SmartTesting ap- proach [10], risk-based test case prioritization based on the notion of risk exposure [11] as well as risk-based testing of open source software [12], in the taxonomy. A taxonomy defines a hierarchy of classes (also referred to as categories, dimen- sions, criteria or characteristics) to categorize things and concepts. It describes a tree structure whose leaves define concrete values to characterize instances in the taxon- omy. The proposed taxonomy is aligned with the consideration of risks in all phases of the test process and consists of the top-level classes context (with subclasses risk driver, quality property, and risk item), risk assessment (with subclasses factor, esti- mation technique, scale, and degree of automation), and risk-based test strategy (with subclasses risk-based test planning, risk-based test design & implementation, and risk- based test execution & evaluation). The taxonomy presented in this chapter extends and refines our previous taxonomy of risk-based testing [3]. The remainder of this chapter is structured as follows. Section 2 presents back- ground on software testing and risk management. Section 3 introduces the taxonomy of risk-based testing. Section 4 presents the selected four recent risk-based testing approaches and discusses them in the context of the taxonomy. Finally, Section 5 summarizes this chapter. 2 Background on Software Testing and Risk Management Software testing [13] is the process consisting of all lifecycle activities, both static and dynamic, concerned with planning, preparation and evaluation of software products and related work products to determine that they satisfy specified requirements, to demonstrate that they are fit for purpose and to detect defects. According to this definition it comprises static activities like reviews but also dynamic activities like classic black or white box testing. The tested software-based system is called system under test (SUT). As highlighted before, risk-based testing (RBT) is a testing approach which considers risks of the software product as the guiding factor to support decisions in all phases of the test process [1, 2, 3]. A risk is a factor that could result in future negative consequences and is usually expressed by its likelihood and impact [13]. In 2 software testing, the likelihood is typically determined by the probability that a failure assigned to a risk occurs, and the impact is determined by the cost or severity of a failure if it occurs in operation. The resulting risk value or risk exposure is assigned to a risk item. In the context of testing, a risk item is anything of value (i.e., an asset) under test, for instance, a requirement, a component or a fault. RBT is a testing-based approach to risk management which can only deliver its full potential if a test process is in place and if risk assessment is integrated appropriately into it. A test process consists of the core activities test planning, test design, test implementation, test execution, and test evaluation [13] (see Figure 1). In the following, we explain the particular activities and associated concepts in more detail. Test Planning Test Design Test Implementation Test Execution Test Evaluation Figure 1: Core test process steps According to [7] and [13], test planning is the activity of establishing or updating a test plan. A test plan is a document describing the scope, approach, resources, and schedule of intended test activities. It identifies, amongst others, objectives, the features to be tested, the test design techniques, and exit criteria to be used and the rationale of their choice. Test objectives are reason or purpose for designing and executing a test. The reason is either to check the functional behavior of the system or its non-functional properties. Functional testing is concerned with assessing the functional behavior of an SUT, whereas non-functional testing aims at assessing non- functional requirements such as security, safety, reliability or performance. The scope of the features to be tested can be components, integration or system. At the scope of component testing (also referred to as unit testing), the smallest testable component, e.g., a class, is tested in isolation. Integration testing combines components with each other and tests those as a subsystem, that is, not yet a complete system. In system testing, the complete system, including all subsystems, is tested. Regression testing is the selective retesting of a system or its components to verify that modifications have not caused unintended effects and that the system or the components still comply with the specified requirements [14]. Exit criteria are conditions for permitting a process 3 to be officially completed. They are used to report against and to plan when to stop testing. Coverage criteria aligned with the tested feature types and the applied test design techniques are typical exit criteria. Once the test plan has been established, test control begins. It is an ongoing activity in which the actual progress is compared against the plan which often results in concrete measures. During the test design phase the general testing objectives defined in the test plan are transformed into tangible test conditions and abstract test cases. Test implementation comprises tasks to make the abstract test cases executable. This includes tasks like preparing test harnesses and test data, providing logging support or writing test scripts which are necessary to enable the automated execution of test cases. In the test execution phase, the test cases are then executed and all relevant details of the execution are logged and monitored. Finally, in the test evaluation phase the exit criteria are evaluated and the logged test results are summarized in a test report. Risk management comprises the core activities risk identification, risk analysis, risk treatment, and risk monitoring [15, 16]. In the risk identification phase, risk items are identified. In the risk analysis phase, the likelihood and impact of risk items and, hence, the risk exposure is estimated. Based on the risk exposure values, the risk items may be prioritized and assigned to risk levels defining a risk classification.

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